Movable anode structure



June 8, 1948.

l. B. BENSEN MOVABLE ANODE STRUCTURE Filed Nov. 10, 1945 Fig.1.

Inventor: Igor B. Bensen,

His Attorney.

Fatenied June 8, 1948 MOVABLE ODE STRUCTURE Igor B. Bensen, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November 10, 1945, Serial No. 627,954

3 Claims.

My invention relates to cathode ray tubes and,

tron optical purposes, such as electron microscopes and electron diffraction instruments, it is desirable to have a narrow beam of electrons for radiating an object being examined. On the other hand, a very narrow beam of electrons is difficult to detect and to focus on a chosen spot -of a specimen and is particularly difficult to center on the fluorescent screen or end wall of the tube. Accordingly, it is a primary object of my invention to provide a new and improved anode structure for a cathode ray tube which provides selectively a broad and a narrow beam of electrons.

It is another object of my invention to provide a new and improved anode for a cathode ray tube having a positionable aperture for controlling the dimensions of a cathode ray beam.

It is still another object of my invention to provide a new and improved anode for a cathode ray tube having a fixed portion and a movable portion and externally accessible means for controlling the position of the movable portion.

An important feature of my invention is the use, in a cathode ray tube used for electron optical purposes, of an anode having a movable portion which includes two apertures of diflerent dimensions and means to vary the position of the movable portion to employ a larger aperture to center the electronic beam of the tube on a fluorescent screen and on a selected spot of a specimen to be examined. Externally accessible means are provided for moving the larger aperture and replacing it with a smaller aperture to define a very narrow beam of electrons for illu'minating or radiating a desired spot of the object under examination.

The aspects of the invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a sectional view of an electron diffraction instrument suitably embodying the invention; Figs. 2

2. vided a glass insulator 4 which serves to support an electron. source in the form of a filamentary cathode 5.-

The cathode is surrounded by an apertured metal member 6 which confines emitted electrons to a beam and which is cooperatively positioned with respect to an apertured anode structure I supported in contact with the main envelope part I. .In the'normal use of the apparatus, the envelope l and the anode l are maintained at ground potential, while the cathode is held at a large voltage below ground potential, such as by connection to a potential source 8 so that the electrons emitted from the cathode are projected through the apertured anode l toward the fluorescent screen 3.

In using the apparatus as an electron difiraction instrument, it is desired to caused the electron stream proceeding from the cathode 5 to produce anarrow beam which normally is centered at the center of the fluorescent screen 3, but which may be caused to scatter, as by reflection from a specimen 9 supported by any suitable manipulating device H) to cause a deflection pattern characteristic of the crystalline structure of the material 9 to appear on the fluorescent screen 3. Alternatively, if the specimen 9 is a very thin layer of a crystalline material, the electron beam may be caused to pass through the specimen to form a re-grouping of the electrons in accordance with a deflection pattern which is characteristic of the crystal. Of course, prior to formation of the electron beam, the region within the container i must be suitably evacuated, as for example by any vacuum pump (not shown) attached to a tubulation II.

- Referring to Figs. 2-4 joinly, I have there shown an enlarged view of the anode structure I of Fig. 1. This structure comprises a circular metallic disk 12 having on one side a'centrally disposed circular recess or shoulder i3 and on its opposite side a longitudinally extending tubular portion it. At the center of the recess 13 there is provided an opening l5 which tapers to the opposite side of the disk l2, and seated in the recess 13' is a circular disk lB having a diameter smaller thanthe diameter of the recess It. The movable disk it is provided near its center with two tiny apertures ll, l8, the purpose of which is pointed out later in this description and which are spaced approximately equal distances from the center of the disk I6. Moreover, the aperture 11 is considerably larger than the aperture [8, having a diameter approximately four times that of theaperture I8. I

The-disk I6 is maintained within the recess l3 andis pressed against thedisk I2 by a retaining arm I 9 secured to the outer surface of the disk [2, and is resiliently biased toward the lefthand side of the anode, as seen in Fig. 2, by a spring formed of any suitable spring material such as beryllium copper. The spring 20 engages at one end a hole 2| inthe'edge' of the disk It and'at its other end" is secured in the hole 22 in the disk [2 by means of a grooved retaining washer 23 and a screw 24.

In order that the disk [8 may be moved to any desired spot in the recess l3 selectively to bring either the aperture I! or theaperture. l8 in the path of the electron beam, I provide means for moving the disk I6 in two rectilinearly disposed directions. This means comprisesa; pairof movable rods 25, 26 which engage the outer edge of the disk It at rectilinearly disposed'posi-- tions. Each of the rodsat its other end carries a roller 2Twhich engages-aninclinedplane surface 28 on a movable piston 29. The piston. :29 is maintained within a cylinder 30 and isresiliently biased toward the right by means. of a spring 3| which is compressed between. the lefthand end of the piston 29 and the. surface of: a retaining cap 32. The cap 32 slides over one end of the cylinder 3fl aI1d-is. attached thereto by means of a: pin 331 The pin.33 likewise passes through a longitudinal slot 34 in the'piston 29 the length of the slot 34-beingequal to theamount of movement required to move the disk It between desired limits. At its other end,.the: piston 29 is provided with an adjustable screw 35' which, in turn, engages a, suitable operating: mechanism, one form of which is illustrated in Fig. 1- asa rack 36 operated by a pinion 31. The pinion 31 preferably is operated by an externally accessible control knob and is provided with a suit.- able bearing arrangement, such as asylphon bellows (not shown) to maintain thevacuum-tight connection betweenithe internal and external operating mechanisms.

The actuating rods 25, 26 preferably lie respectively in radially extending slots 38, 39 in the disk [2 and areretained in these slots by a plate 40 which is aflixed to-the disk [2 by aplurality of screws 4L As previouslyexplained, the entire anode structure fits within the metallic container l and may be providedwithan orienting. tab 42 to assist in locating. the structure in the desired longitudinal and angular positions.

Intheoperation of electron diffraction instruments of Fig. 1, it is desired, prior to obtaining a diffraction pattern, to center the cathode ray beam on the fluorescent screen 3. To this end. the cathode ray beam emitted by the filamentary cathode 5 is allowed-to pass through the larger aperture I I and to be focussed by means of a focussing yoke (not shown) to fall upon the center of the fluorescent screen 3. Thereafter, an object to be examined is placed in the pathoi this beam by means of manipulator It! so that the beam either passes through the object, in the case of a very thin object, or is reflected therefrom at a desired angle. For optimum definition of the diffraction lens of the pattern, it is desirable that a very narrow beam of electrons be used. Accordingly, after the object has been oriented by means of the manipulator l0 so that the beam falls upon a desired spot,.the anode disk is moved in a substanti-ally rectilinear motion by means of the two rods 25, 26 actuated by the piston 29 to move the aperture IT from the center of the path of the electron beam and. to replace it with the smaller aperture l8. Due to the effect of the spring 20, the motion imparted to the disk l6 by the rods 25, 26 is slightly rectilinear. However, due to the extremely small distances involved which are of the 'orderof20 toz-40 millimeters, substantial rectilinear-motion is imparted to the disk I6.

An important advantage of my improved anode structure is-v that it clearly facilitates the centering of the beam in an electron difirac-tion instrument. Thus, bythe use of a larger aperture H, which may be of "the order of 10 millimeters, it is relatively easy to obtain a spot upon the fluorescent screen 3 -and to center that spot by means of a focussing yoke. Thereafter the disk I6 is moved by means of the rods 25, 26 until the large spot due to the aperture I'I passes off the screen and. is replaced: by a considerablyv smaller spot due'tothe-aperture I8. All manipulationsv are effectedby easily-controlled knobs outsidethe diffraction instrument. and, throughout its movement, the disk [6 is pressed against the-anoderdisk l2 sothat no variations involtage of the disk lfi'areobtained to afiect the focus of the electron beam.

While my inventionhas been describediby. reierenceto a particular embodiment thereof,.it will be understood that numerous modifications-may be made by those: skilled in.the art without actually departing from. the invention. 1- therefore aim in the appended'claims tocover all such modifications as fall within the. true spirit and scope ofthe foregoing disclosure.

What I claim as new and desire to. secure by Letters Patent of the United-States is:

l. The combinatiomin a cathode ray tube, of an enclosingv envelope, an anode supported with.- in said envelope, saidanode comprising a fixed portion, a movable portiom, means maintaining anelectrically conductive connection between said portions, and means whereby the position of said movable portionmay be varied.

2. A cathode ray tube comprising an enclosin envelope, means for producing a cathode ray beam, an.- anode structure supported. within said envelope, said structure including. a, fixed portion anda movable. ortion, means external to said envelope for selectively varying the. position of said movable portion, and means maintaining conductive connection between said portions as said positionis varied.

3; The combination, in-an electron optical instrument, of an evacuated envelope, means within said envelope for producing a cathode ray beam, an anode supported within said envelope, said anode comprising. a. fixed portion and a movable portion, said movable. portion having a pair of apertures therein, aviewing. screen, and externally accessible means. for moving said. movable portion to direct saidcathode beam through a selected one of said apertures to said screen.

IGOR B. BENSEN.

REFERENCES: CITED The following references are of record in the file of this patent? UNITED STATES PATENTS Number Name Date 2,247,524 Schuchmann et al. Jul'y'l, 1941 2,290,53I Brett July 21, I942 2,352,043 Von Ardenne June 20, 1944 

